A powertrain of a vehicle generates drive torque and transfers the drive torque to a drivetrain using a transmission. Examples of torque generating systems of the powertrain include an engine, an electric motor, and combinations thereof. For automatic transmissions, a vehicle control system (e.g., a controller) schedules and executes gear engagement operations between the torque generating system and the transmission. One primary goal of vehicle control systems is to perform gear engagement operations that are not noticeable to the driver. That is, any noise/vibration/harshness (NVH) or “clunk” caused by the gear engagement operations, such as a physical jerk of the vehicle or a loud sound, should be avoided or mitigated.
One scenario where clunk may occur is while in a higher gear (e.g., 5th gear) of the automatic transmission and after accelerator pedal tip-in and tip-out events. After a pedal tip-out event, the powertrain torque request quickly decreases to zero and the actual torque output of the powertrain is zero or negative. This negative torque output means that the transmission is driving the powertrain, e.g., the engine's crankshaft or an electric motor. After a pedal tip-in event, the powertrain torque request quickly increases and the actual torque output of the powertrain increases to a positive value.
These pedal tip-in/tip-out transitions result in clunk. As shown in FIG. 1A, an engine/motor shaft 10 is typically driving a transmission shaft 12 in a first direction via respective gears 14, 16 each having a plurality of respective teeth 18, 20. After a pedal tip-out event, the transmission shaft 12 eventually begins driving the engine/motor shaft 10 in an opposite second direction as shown in FIG. 1B. This harsh or abrupt teeth-to-teeth contact causes clunk. Similarly, after a subsequent pedal tip-in event, the engine/motor shaft 10 begins driving the transmission shaft 12 in the first direction again (see FIG. 1A), which again causes the teeth 18, 20 to contact each other at contact point 22 as shown in FIG. 1C. This abrupt contact between the teeth 18, 20 causes clunk 24 (see FIG. 1C), which could comprise physical vibration and/or audible noise.
Conventional vehicle control systems command an instantaneous torque request in response to a pedal tip-in or tip-out event. By decreasing the rate of change of the torque request, clunk could be mitigated or eliminated. Conventional vehicle control systems, however, utilize spark retardation to temporarily reduce engine torque and generate a torque reserve. Spark retardation, however, increases exhaust gas temperature, when has potential negative effects the life of the vehicle's catalytic converter, brake-specific carbon monoxide (BSCO) or similar emissions (e.g., hydrocarbon (HC) slip), and/or fuel economy. Accordingly, while such vehicle control systems work for their intended purpose, there remains a need for improvement in the relevant art.